1. Field of the Invention
The present invention generally relates to an antenna system in a BS (base station). More particularly, the present invention relates to an array antenna system for forming horizontal and/or vertical beam radiation patterns individually.
2. Description of the Related Art
Unlike a wired channel environment, a wireless channel environment in which a mobile communication system exists distorts a real transmission signal due to many factors including multipath interference, shadowing, propagation attenuation, time-variant noise, and interference. Fading caused by the multipath interference is closely related to signal reflections resulting from the mobility of a user, i.e. a user terminal. With the fading, a received signal includes a real transmission signal and an interference signal in combination. The fading phenomenon is a significant factor that impairs high-speed data communication in the wireless channel environment, because it may distort the amplitude and phase of the received signal. Many studies have been conducted to solve the fading phenomenon. In this context, it can be concluded that signal loss caused by the nature of mobile communication channels such as fading and user interference should be minimized to transmit data at high rates in the mobile communication system.
To physically improve uplink gain, BS antenna systems adopt reception diversity. From the software perspective, they use a technique for obtaining a processing gain using a rake receiver.
The recent need for further securing an uplink/downlink gain due to the increase of the complexity of transmission schemes has driven independent development of Multiple Input Multiple Output (MIMO)-based and smart antenna (adaptive array antenna)-based techniques. Now the developmental trend is to use the two techniques in conjunction by combining the physical and software schemes.